This is a continuation application to study the involvement of the low affinity receptor for IGE (FceRII/CD23) in Type I allergy and inflammatory cytokine release. Two STAT6 sites have been identified in the murine CD23 gene; one in the promoter region of murine CD23a and another in intron-2 in the CD23b promoter equivalent region. The role of the two sites in cooperative upregulation of CD23 will be determined. In addition the role of a number of other DAN-binding protein motifs are present in the CD23a promoter. Special attention will be on murine transcription factor E3 (mTFE3) as knockout animals have no constitutive expression of CD23 and NFkB since destruction of the putative NFkB site has been shown to abrogate CD23 promoter reporter expression. The activity of this site for interaction with NFkB will be determined in gel shift and supershift assays and the potential for IL-4 to activate NFkB will be determined. CD23 plays a role in both oligomerization and potentially in interacting with IgE. This knowledge will be used to prepare oligomeric CD23 chimeras that have full IgE binding activity. Such constructs could potentially represent a novel method for isotype-specific regulation of IgE. Culture of B cells with membrane CD23 has been shown to inhibit B cell growth and Ig, especially IgE, production. Development of a soluble construct with full IgE-binding activity will allow the mechanism of this CD23-mediated effect to be studied in greater detail. Analysis of Ig production suggests that the order of sensitivity to high CD23 is IgE>IgG1>IgM and the observation that levels of germline transcript are not affected directs attention at post-switch development of the B cell. Special attention will be directed at the possibility that high CD23 can induce apoptosis in B cells and this will be examined in TUNEL or equivalent assays. Comparison of the effects of oligomeric vs monomeric sCD23 constructs will be performed. Finally, evidence has been obtained that an oligomeric sCD23 construct can induce IL-6 release from macrophages and macrophage cell lines. The structural characteristics of CD23 required for the inflammatory cytokine release will be determined. New knowledge from these studies may help in the development of new treatments for Type I allergy and for control of inflammatory cytokine release.